Water-in-oil tester



FIG. 1 is a front perspective view of a water-in-oil tester showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a left side elevational view thereof; and

FIG. 5 is a right side elevational view thereof. 

The ornamental design for a water-in-oil tester, substantially as shown. 